This 13-tooth upper and 19-tooth lower OSPW system has been tested in competitions such as Paris-Roubaix, Strade Bianche, and CX World Cups. The system is designed for gravel and cross disciplines and meets the demands for durability, low friction, and longevity. The four spring tension adjustments allow for custom configuration based on riding conditions, and the hand-built OSPW system features a custom-molded carbon fiber cage for lightness and robustness. CeramicSpeed OSPW systems reduce friction by 35-40% compared to standard pulley configurations. Compatible with specific 2X RX820 and RX825 derailleurs. If using a 1x system, a maximum 36T cassette can be used. Note: with the RX825 Di2 derailleur, only the H (high) spring tension hole must be used. In the package: Complete OSPW X System for Shimano GRX RX-820 2x12 CeramicSpeed UFO TECH Bearing Oil 15 ml dropper bottle for pulleys.